An Exploit (from the verb to exploit, in the meaning of using something to one’s own advantage) is a piece of software, a chunk of data, or sequence of commands that takes advantage of a bug, glitch or vulnerability in order to cause unintended or unanticipated behaviour to occur on computer software, hardware, or something electronic (usually computerised). Such behavior frequently includes such things as gaining control of a computer system or allowing privilege escalation or a denial-of-service attack.

Classification

There are several methods of classifying exploits. The most common is by how the exploit contacts the vulnerable software. A 'remote exploit' works over a network and exploits the security vulnerability without any prior access to the vulnerable system. A 'local exploit' requires prior access to the vulnerable system and usually increases the privileges of the person running the exploit past those granted by the system administrator. Exploits against client applications also exist, usually consisting of modified servers that send an exploit if accessed with client application. Exploits against client applications may also require some interaction with the user and thus may be used in combination with social engineering method. Another classification is by the action against vulnerable system: unauthorized data access, arbitrary code execution, denial of service.

Many exploits are designed to provide superuser-level access to a computer system. However, it is also possible to use several exploits, first to gain low-level access, then to escalate privileges repeatedly until one reaches root.

Normally a single exploit can only take advantage of a specific software vulnerability. Often, when an exploit is published, the vulnerability is fixed through a patch and the exploit becomes obsolete for newer versions of the software. This is the reason why some blackhat hackers do not publish their exploits but keep them private to themselves or other hackers. Such exploits are referred to as 'zero day exploits' and to obtain access to such exploits is the primary desire of unskilled attackers, often nicknamed script kiddies.

Types

Exploits are commonly categorized and named by these criteria:

The type of vulnerability they exploit (See the article on vulnerabilities for a list)

Whether they need to be run on the same machine as the program that has the vulnerability (local) or can be run on one machine to attack a program running on another machine (remote).

The result of running the exploit (EoP, DoS, Spoofing, etc.)

Pivoting

Pivoting refers to method used by penetration testers that uses compromised system to attack other systems on the same network to avoid restrictions such as firewall configurations, which may prohibit direct access to all machines. For example, an attacker compromises a web server on a corporate network, the attacker can then use the compromised web server to attack other systems on the network. These types of attacks are often called multi-layered attacks. Pivoting is also known as island hopping.

Pivoting can further be distinguished into proxy pivoting and VPN pivoting:

Proxy pivoting generally describes the practice channeling traffic through a compromised target using a proxy payload on the machine and launching attacks from this computer. This type of pivoting is restricted to certain TCP and UDP ports that are supported by the proxy.

VPN pivoting enables the attacker to create an encrypted layer 2 tunnel into the compromised machine to route any network traffic through that target machine, for example to run a vulnerability scan on the internal network through the compromised machine, effectively giving the attacker full network access as if they were behind the firewall.Typically, the proxy or VPN applications enabling pivoting are executed on the target computer as the payload (software) of an exploit.

Remote Exploit

Remote Exploit allow hacker to get access on a server. Depending on what service is exploited, hacker will get user or root privileges on the exploited server. Some times, it is user privileges, then hacker scan the server for any known Local Exploit, if he found one, he use that to get root access on the server. Once hacker get root access they install rootkit (backdoors), that allow him to login and work on the server with out tracked by server administrator or other users.

A common way to classify attacks is whether they are done remotely by a hacker from across the Internet, or whether they are done locally by a user who already has privileges on the system. The important difference is that a "remote" attack can be launched by any of the hundreds of the of millions of people on the Internet at any time without first logging on. Point: A hacker may need to use a combination of remote and local exploits in order to gain control over a system. More and more services are running within sandboxes in order to limit the "spread of the infection". A local exploit may be needed in order to break out of the sandbox. Key point: The most common remote exploits are buffer overflow and other unchecked input attacks. They are either done against public services (such as HTTP and FTP) or during the logon of protected services (such as POP and IMAP).